Definition
A Latin term from the civil law tradition meaning an accessory thing — something that belongs to, is connected with, or depends upon another thing as its principal (res principalis). The accessorium is the lesser element that attaches to and follows the more significant thing, whether in matters of property, contract, or obligation.
The governing maxim is: accessorium non ducit, sed sequitur suum principale — the accessory does not lead, but follows, its principal. The practical consequence is that whatever legal regime attaches to the principal thing governs the accessory as well. The accessory cannot be transferred, extinguished, or adjudicated independently of the principal unless the law expressly provides otherwise.
Common Confusion
ACCESSORIUM vs. ACCESSORY (criminal law): These terms share a Latin root but operate in entirely different legal domains. Accessorium is a property and obligations concept from the civil law — it describes a thing's relationship to another thing. An accessory in criminal law describes a person's relationship to a crime. Researchers encountering accessorium in historical civil-law sources should not carry criminal-law connotations into the analysis.
ACCESSORIUM vs. APPURTENANCE: These concepts overlap but are not identical. An appurtenance typically denotes something physically attached to or habitually used with land. Accessorium is the broader civilian concept and can apply to obligations, rights, and personal property — not only real property. In sources influenced by English common law, appurtenance often displaces accessorium as the operative term.
Core Elements
The concept rests on three structural propositions:
1. Dependence: The accessorium has no legal existence independent of its principal. It cannot stand alone.
2. Subordination: The accessorium follows the fate of the principal — if the principal is sold, transferred, extinguished, or encumbered, the accessorium goes with it.
3. Non-leadership: The accessorium cannot determine the legal character of the transaction. The principal sets the terms; the accessory conforms to them.
Why It Matters in Research
Researchers working in civil-law-influenced jurisdictions — Louisiana, Quebec, the mixed systems of South Africa and Scotland, and historical Spanish and French colonial legal materials — will encounter accessorium as a live doctrinal term, not merely a Latin flourish. In those contexts, the accessorium principle actively governs questions of mortgage, servitude, and contract: a security interest (accessorium) cannot outlive the debt it secures (principale).
In common-law materials, the concept surfaces mainly in maxim form — accessorium sequitur principale — cited in equity, property, and conflict-of-laws disputes to justify treating subordinate rights as following dominant ones. Common-law courts rarely use the Latin noun accessorium itself; they borrow the maxim while translating the concept into common-law vocabulary (appurtenance, incident, ancillary right).
The principal trap for historical corpus researchers is inconsistency of spelling and abbreviation. Sources may render the term as accessorium, accessorius, or accessory interchangeably, and Anderson's Dictionary cross-references the concept under ACCES- without completing the entry — a known truncation in that source. When tracing the maxim through Bracton and Fleta (both cited by Burrill), researchers should be aware those are medieval common-law compilations working with civilian concepts, meaning the term appears in a hybrid doctrinal context that is neither pure civil law nor standard common law.
Historical Dictionary Support
The three shelf sources agree on the core meaning but reflect different orientations. Burrill's is the most thorough, supplying the civilian lineage (Calvinus's Lexicon Juridicum, Cowell, Bracton, Fleta) and correctly identifying the term as a noun of the civil law with the parent verb accedere (to go to, or with). Black's treats the term instrumentally, offering only the maxim and Coke's citation, which reflects Black's consistent preference for maxim-as-entry over substantive civilian analysis. Anderson's is the most abbreviated and, as noted, cuts off mid-cross-reference — a gap that makes it unreliable as a standalone source for this term.
None of the three sources provides a worked example of how the accessorium principle resolves a concrete dispute, which limits their utility beyond establishing the term's existence and its governing maxim. Researchers needing doctrinal application should move from these dictionary entries into the civil-law treatise tradition.
Jurisdictional Note
The accessorium principle operates most explicitly in civil-law and mixed jurisdictions. In Louisiana, for example, the principle that an accessory obligation follows the principal is codified in the Civil Code. Common-law jurisdictions apply equivalent reasoning but rarely use the term, preferring language of incidents, appurtenances, or ancillary rights.
Encyclopedia Cross-Reference
See Law Mind Encyclopedia: Accessory and Principal (Property); Maxims of Law; Civil Law Tradition in American Jurisdictions